The invention relates generally to the field of semiconductor sensors. More particularly, the invention relates to a stress sensor based on hybrid materials and methods of making the same.
Tactile sensors have gained renewed interest as the level of sophistication in the applications of humanoid robotics and minimal invasive surgery increases. Most robotic systems incorporate binary touch sensors that can distinguish between touch and no touch. To improve the manipulative capabilities of robotic hands, more sophisticated tactile sensors that can replicate the sensation of touch are needed. That would require the development of a device that can be mounted on a curved surface and sense a distribution of contact stress as low as 10 kPa at a high spatial resolution of about 40 μm over a contact area of ˜1 cm2. Many technologies have been explored for tactile sensing, including conducting elastomers, piezoresistive materials, and micro-electro-mechanical systems. However, their use in dexterous hands are hampered due to two limitations: (i) poor spatial resolution lagging by one order of magnitude compared to a human finger; and (ii) strain-induced nonuniform background signals in devices built on large curved surfaces due to the lack of flexibility. Recently, a new tactile sensor consisting of alternating layer of nanoparticles and dielectric materials was demonstrated. The sensor was capable of imaging stress distributions with a high spatial resolution, but its practical use may be limited by the complexity of the device structure and processing.
Organic and polymeric materials are flexible and sensitive to external stresses. Upon compression, their resistivity may change dramatically due to reduced intermolecular distance and increased orbital overlap which lead to higher rates of electron transfer between neighboring molecules. This sensitive piezoresistive response to deformation makes them attractive materials for stress sensing applications. In addition, many organic and polymeric dyes have superior fluorescent or phosphorescent properties, and have been used to develop high-efficiency organic light-emitting diodes (OLEDs). The quantum efficiency of OLEDs is largely dependent upon carrier tunneling and energy transfer processes, whose rates are strong functions of the intermolecular distance. Therefore, organic and polymeric thin films may respond to applied forces with changes in current density as well as luminescent emission. Given these unique behaviors, along with easy fabrication and compatibility with flexible substrates, it is possible to use organic and polymeric thin films to build simple and low-cost tactile sensors which are capable of high-resolution imaging of stress distributions (stress fields).
The present invention employs a hybrid light-emitting diode structure as tactile sensing devices by utilizing their sensitive and repeatable responses to stresses with changes in current density as well as electroluminescent light intensity. These devices find use in many other fields, including biometrics and medial applications.